Due to mechanical limitations, milling machines fail to reproduce 100% of the design.
The advent of the CAD/CAM era has brought many conveniences, but sometimes mechanical limitations stand in the way of our efforts. As an example, I designed a difficult case of anterior teeth in exocad. I created gum because of receding gums. I put significant efforts into making it a very beautiful design. However, the milling result was not what I intended. I was very disappointed that it was incorrect. I realized that no matter how hard I designed, it couldn’t be reproduced 100% because of the mechanical limitations of milling machines.
Most milling machines only mill at 0 and 180 degrees. There are not many milling machines that the A-axis turns completely even the machines are 5-axis. These milling machines are focus on undercuts of inner sides, not the external sides. Now, let me explain about 90-degree milling, which has a significant effect on the accuracy of the milling machine.
The anterior teeth are more important for aesthetics than for function.
I think that functional parts are more important than aesthetic parts for the occlusal surfaces of the posterior teeth. However, anterior teeth are different. The anterior teeth are aesthetic. Of course, functional parts are important, but aesthetic parts are more important because these are the anterior teeth.
Requirements for 90 degrees milling
C-clamp reproduces everything over mechanical limitations.
The C-clamp could reproduce everything that I designed over mechanical limitations. The C-clamp is a C shaped clamp that holds a zirconia block. There’s no interference from the milling tool when the A-axis rotates because one side of the clamp is open. This is why CRAFT 5X can mill at 90 degrees.
The machine mills the textures formed on the labial side, the interproximal area, and the gingiva lines with all details. I also design gums with protheses for the patient with receding gums. Even I design gingiva beautifully in CAD program, most of the milling machines cannot mill the gingiva lines. So I have to trim the zirconia block again like contouring before sintering. Moreover, there are micro cracks or other problems while trimming the zirconia block.
Precise motor and sturdy frame body
I am sure some of you are wondering that all milling machines with the C-clamp can mill at 90 degrees. I would like to say that it is not. The precision of the milling machine is very important for the 90 degree milling. To support this precision, there are two important factors. First, a very precise motor. Second, a very sturdy frame body. Only when these two conditions are fulfilled, we get the precision.
There are lines on crowns because of gaps which are formed when the precision is not supported even with the 90degree milling. Then, you need to contour to trim the lines. But with a precise milling machine, you rarely trim the lines. So before you buy a milling machine, you should always check how accurate the motor is and whether the frame body is assembled or not.
90 degree milling with CRAFT 5X
Let’s take a look to see how the 90 degree milling works with CRAFT 5X. This is a case that I worked on before.
After open a file, change the frame to the C type.
Turn the labial side up and place it to the top.
Remove all connectors on the buccal side. Select the 90 degree milling template and the type with 90 at the end.
Choose dry or wet milling. I’m going to choose dry milling. Next, choose the direction of the spindle. It’s best to have a spindle coming in from the front. Open “Identify part features” windows and select User-defined area.
After selecting the type, click the “Draw contour” button and select the area for the 90 degree milling like the image below.
Click the “Accept” and “Close” buttons. The insert direction is marked with a purple arrow in the red circle.
It means the spindle comes down this direction and begins to mill. Now, click the Calculate toolpaths button.
I have made two cases.
One is done with the 90 degree milling that the labial surface milled completely. Another one is the same case, but it’s only milled at 0 and 180 degrees. I have prepared these two cases to clarify. As you can see, the case on the left is with the 90 degree milling. You can see the big difference between these cases within the gingiva lines and the interproximal areas.
We have looked at the 90 degree milling today. It is not a good milling machine if it cannot reproduce 100 % of your elaborate designed cases. In my case, my design is almost perfectly reproduced by the 90 degree milling, so accomplishment and satisfaction have increased in double. I hope you can also feel this accomplishment and satisfaction with CRAFT 5X.
Thank you for reading my lecture! See you later.